Self-leveling and grade setting laser apparatus

Abstract

A pivotally-mounted laser or other collimated light beam source is maintained in a level position by means of a thermal motor capable of precise small movements. Actuation of the motor is accomplished by a control amplifier whose inputs are responsive to the output of a level-sensitive transducer. Pre-selected grades may be established and maintained by means of a second thermal motor which is employed to change the angular relationship between the pivotally mounted laser or light source and the level-sensitive transducer.

What is claimed is: 
     
       1. An apparatus for automatically maintaining the angular position of the light beam produced by a light source, comprising: a base;   pivotal mounting means attached to the base, for mounting the light source;   a thermal motor having a heating coil and having two ends the linear displacement between which is responsive to the current applied to the heating coil, one end of said thermal motor being attached to the base and the other end being attached to the cradle;   a level-sensing transducer having electrical signal outputs which are indicative of the displacement of the transducer with respect to a level position, and;   control means connected to the heating coil of the thermal motor for producing a current in said heating coil in the proper magnitude and phase relationship such that a displacement in the position of the level-sensitive transducer is corrected by a corresponding displacement in the thermal motor such that the original position of the level-sensitive transducer is maintained.   
     
     
       2. The apparatus of claim 1 including means for mounting the level-sensitive transducer such that the angular displacement between the transducer and the light source may be varied. 
     
     
       3. The apparatus of claim 2 wherein the means for pivotally mounting the level sensitive transducer is a transducer mount which is pivotally afixed to the cradle. 
     
     
       4. The apparatus of claim 3 including a second thermal motor having characteristics similar to that of the first thermal motor and having one end attached to the cradle and the other end attached to the level-sensitive transducer mounting means. 
     
     
       5. The apparatus of claim 4 including a thermal sensor used to determine the interior temperature of the second thermal motor. 
     
     
       6. The apparatus of claim 5 including means for setting linear displacement of the second thermal motor by establishing and maintaining a selected internal temperature of the thermal motor. 
     
     
       7. The apparatus of claim 6 including control means connected to the heating coil of the thermal motor and responsive to the thermal sensor for producing a current in the heating coil in the proper magnitude and phase relationship such that changes in the ambient environment tending to cause a change in the internal temperature of thermal motor are offset by a corresponding change in the current applied to the heating coil, so that the internal temperature of the thermal motor remains constant.